"They said, 'We love your foundation and want to do a promotion with you,' " he said.

The upshot: Vetri and Shake Shack culinary director Mark Rosati collaborated on a carbonara burger (beef, bacon, pecorino cheese, black pepper, sunny-side-up egg), which will be sold at the Philadelphia-area Shake Shacks from June 6 to 15 for $6.75.

One dollar from each sale will go to the Vetri Foundation, whose mission is childhood nutrition. It's Shake Shack's first such collab with a local chef.

After the promotion, Vetri plans to put the burger on Alla Spina's menu.